1. Field of the Invention
The present invention relates to a camera system that functions to communicate data between a camera body and a photographing lens.
2. Description of Related Art
In a recent single lens reflex camera having an automatic focusing device, information peculiar to a photographing lens, such as open F-number data used in an automatic exposure function or an automatic focusing function is sent as electrical signals from the photographing lens to a CPU (central processing unit) of a camera body.
Information peculiar to the photographing lens is stored in a lens ROM provided in the photographing lens. The photographing lens and the camera body are provided with electrical contacts on a lens mount and a body mount to transmit and receive signal information between the photographing lens and the camera body, respectively. The body CPU transmits and receives the signal information to and from the lens ROM through the electrical contacts and reads the data stored in the lens ROM. A clock pulse is outputted from the camera body to send address signals from the body CPU synchronously therewith, so that predetermined data can be output from the lens ROM in accordance with the address signals.
However, in an arrangement in which a motor is also provided in the photographing lens to control the power zooming etc., if all the control operations in the photographing lens are effected by the body CPU, there will be an overload thereon. In particular, in a single lens reflex camera in which various kinds of photographing lenses are exchangeably mounted to the same camera body, the body CPU must read different parameters, depending on the photographing lenses from the associated lens ROM, and perform predetermined arithmetic operations in accordance with the read parameters to thereby control the photographing lenses. This makes quick operations impossible or next to impossible.
In addition to the foregoing, in a case where the photographing lens to be mounted to the camera body is, for example, a macro lens in which macro-photographing can be carried out, various data, including a drive pulse coefficient K value (number of pulses `conversion coefficient` corresponding to a displacement of the lens per unit defocus amount, necessary for AF control of the zoom lens by an AF motor) necessary for macro-photographing, etc., are stored in the ROM of the macro lens. Therefore, the stored data must be partially erased, or a large ROM must be used instead of a conventional ROM to write new data.